This invention relates to an electrohydraulic switching device for generating electrical control signals as a function of pressure signals applied thereto.
A known switching device of this type consists of a housing, and a piston guided in an axially displaceable manner in the housing. One of the piston ends carries an actuating plate for actuating an electric switching mechanism, as well as of a guide sleeve locking a cylinder bore within the housing and having a tubular extension. The piston is provided with a plastic sealing ring which prevents pressure medium from flowing from the hydraulically pressurized side into the cylinder bore within the housing. Arranged in the cylinder bore is a compression spring which supports itself with one of its ends at a spring plate, while at the other end it is axially guided by the tubular extension of the guide sleeve. A snap ring secures the spring plate against axial displacement against the direction of actuation of the piston. The snap ring is supported in a square groove of the piston. A screw screwed into a respective threaded bore within the piston end holds the actuating plate at the piston end facing the electric switching mechanism. Further, the actuating plate has a cylindrical guide portion slidingly guided within the tubular extension of the guide sleeve.
As it is impossible to ensure a satisfactory sealing of the cylinder bore when using the plastic sealing ring, a gasket is provided which is seated in an outside circumferential groove of the piston and the sealing lips of which rest against the inside wall of the tubular extension of the guide sleeve. Along with a sealing ring supported in a circumferential groove of the guide sleeve, the gasket serves to seal the cylinder bore hydraulically with respect to the housing chamber accommodating the switching mechanism. Sheared-in indentations hold the guide sleeve in the housing at four points.
In the known switching device, however, it has been noted that during a pressurization of the piston and during the piston movement ensuing thereupon, frictional forces occur both between the sealing lips of the gasket and the inside wall of the tubular extension of the guide sleeve and between the inside wall and the cylindrical guide portion of the actuating plate. The frictional forces have a negative influence on the switching behavior of the switching device. Further, due to the manufacturing tolerances of the individual components, there is a danger that the spring plate stamped out of sheet metal will be deformed by the action of the strong force of the compression spring so as to be caused to slide beyond the snap ring, thus leading to the destruction of the entire switching device.
It is thus an object of the present invention to provide an electrohydraulic switching device of the type referred to above wherein the friction is minimized. At the same time, the switching device shall be of simple design and allow low manufacturing cost.